My research deals with molecular processes in cutaneous cells that affect the expression of genetic information, and in the manner in which these processes are reflected in skin function. This project explores the defenses of cutaneous cells to photomediated DNA injury by ultraviolet irradiation. The shielding effects of melanin pigment to cells of irradiated skin as well as to individual cells irradiated in culture are examined with respect to cell viability, damage to DNA, DNA replication, cell division and pigment production. Pigmented and non- pigmented melanoma cells as well as fibroblasts are used in these experiments. The production of thymine dimers (by 260 nm UV light) and of 4,5'8 trimethyl psoralen (TMP) cross-linking photoadducts (by 360 nm UV light) are quantitatively measured in DNA extracted from irradiated cells. The DNA-repair mechanisms that remove TMP cross-links in different types of cutaneous cells are sought with emphasis on excision and recombination steps. Experimental methods employed include two- dimensional paper chromatography, hydroxyapatite column chromatography, autoradiography, zone sedimentation in sucrose gradients and equilibrium centrifugation in density gradients. This work deals with protection against potentially mutagenic and carcinogenic damage to DNA by UV light.